Simple network management protocol (SNMP) is a system for monitoring and managing computer systems and components over a network. An SNMP management station communicates with SNMP agents that directly monitor or control devices or components in the system.
The SNMP agents provide access to monitored device data as a set of variables. Device data that can be monitored by an agent can include an amount of free memory in a system and a number of running processes on that system. The SNMP management station can access the monitored device data through a set of defined protocol operations including the GET, GETNEXT and GETBULK protocol operations. The SNMP agent can also send data to the SNMP management agent using the TRAP or INFORM protocol operations.
The data accessible via SNMP is organized into a hierarchy. The hierarchy and other metadata, including the type and description of the variables, are described by management information bases (MIBs). MIBs describe the structure of the monitored data and its position in the hierarchy. The MIBs use a hierarchical namespace containing object identifiers (OID) to identify each monitored variable. Each OID uniquely identifies a variable that can be read via SNMP operations.
The hierarchy of the OID namespace is a tree, the levels of which are defined by different organizations. The highest or top portion of the hierarchy of OID namespace is defined by or assigned to respective standards organizations, while the namespace of a lower portion of OIDs is defined by vendors or other organizations.
The OID is a parameter of the various SNMP operations. Thus, when a user of an SNMP management station want to obtain data about a specific component, the user specifies the OID of that component. The SNMP management station generates the appropriate SNMP operation (GET, GETNEXT GETBULK) to retrieve the data passing the OID as a parameter to the operation. The SNMP agent receives operation, looks up the data using the OID and generates a response with the requested data that is identified by the OID.